The field to fill from is Ses:SessionTimes and the Sessions file contains time values (as strings) like 01:00 AM, 01:30AM, etc. This file also contains a second field called MilitaryTimeforKey, that is used to keep the times in the appropriate order using the key named KeyMilitaryTime.
The Target Field is Sch:SessionStartTime and is a string value that is to be updated by the Combo control.
I selected a key (KeyMilitaryTime) for the file (SessionTImes) containing the selections that should be in the drop list. I did not select a key for the record to be updated (ScheduleDatesMachines) with the data from the Combo box.